The getgrgid_r function updates the group structure pointed to
    by grp and stores a pointer to that structure at the location
    pointed to by result. The structure contains an entry from the
    group database with a matching gid. Storage referenced by the
    group structure is allocated from the memory provided with the
    buffer argument, which is bufsize characters in size. The maximum
    size needed for this buffer can be determined with the _SC_GETGR_
    R_SIZE_MAX parameter of the sysconf function. On error or if the
    requested entry is not found, a NULL pointer is returned at the
    location pointed to by result.